Process for dyeing of suede



Patented Au 6, 1946 PROCESS FOR DYEING OF SUEDE Foster Lewis Pepper, Glenside, Pa., assignor to American Cyanamid Company, New York, N. Y., a corp r ion of Maine No Drawing. Application April 1, 1942, Serial No. 437,193

8 Claims. 1

This process relates to a new and improved method of dyeing suede leather.

Suede leather is usually mad from calf or kid skins which have been chrome tanned and finished on the flesh side. This produces a very porous leather which is easily penetrated by dyes and therefore can be readily dyed a full shade with developed dies. These developed dyes comprise certain of the amino-azo dyes which still have a diazotizable group. A dye of this type can be applied to the leather and then diazotized and coupled in situ using a developer such as an amine or a phenol to produce a very full shade.

The conventional and best known method of applying these developed dyes to leather involves a number of steps, in the carrying out of which some five or six different baths and a number of washing steps are used. The first step usually comprises placing the leather in a drum and wetting out with an alkaline solution for a considerable period of time. After this wetting out period the drum is dumped and the solution is replaced by a fresh, slightly alkaline bath which has been preheated to about 130 F. An aminoazo dye is added to this bath and allowed to penetrate the leather. Customarily this dye penetration step is carried out in two stages, only a part of the dye being added at each stage. After the second dye-penetration stage an organic acid, usually formic acid, is added to exhaust the the dye on th skins and the drum is again drained.

The skins are then cooled to about 60-65 F., and subjected to treatment with a strong acid and sodium nitrite to diazotize the dye. After the diazotization step the skins are again drained but still contain an undesirable excess of nitrous acid, which if not removed will interfere with the developer and produce an off-shade color. The leather is therefor thoroughly washed a number of times to remove the nitrous acid. A developer is then added and coupled with the diazo, after which the leather is again washed and fatliquored to complete the process.

Although the conventional process will produce a satisfactorily dyed suede leather of a good full shade it possesses several distinct disadvantages. The large number of different baths, the many draining and washing steps are wasteful, both of time and materials. There is a very appreciable loss of both acid and alkali. Considerable time and large quantities of ice are required to reduce the temperature of the leather after the dye xhaustion step since the diazotization step must be carried out in the cold. After diazotization the dye is in a water soluble condition and the repeated washing steps to remov excess nitrous acid cause the loss of large amounts of the dye. Often as high as 40% of thedye is lost in this way after the trouble and expense of exhausting it on the leather and diazotizing it in situ. Further, the process requires approximately 6 hours, so that two complete batches can not be run by one operator in an 8 hour shift, which is a considerable disadvantage from a practical point of view.

In general, the present invention comprises carrying out a similar dyeing procedure in a single bath cold process making use of the same acid for the diazotization step that was used for exhausting the dye. This produces a considerable saving in materials used and enables the production of the same full shade of color in a much shorter length of time so that two runs can be easily made in an 8 hour shift.

In carrying out the process of th present invention the skins are placed in a rotating-drum, wet with a cold alkaline solution such as ammonium hydroxide and an amino-azo dye is immediately added to the drum so that the wetting out and dye penetration steps are carried out simultaneously in the cold rather than as several steps at different temperatures as in the conventional process. A strong mineral acid is then added to the same cold bath to exhaust the dye on th skins and after allowing a short time for the acid to exhaust the dye, sodium nitrite is added to the drum and the diazotization carried out making use of the same mineral acid. This eliminates the steps in the conventional process of washing out the formic acid, cooling the skins, and replacing the formic acid with the mineral acid necessary for diazotization.

Instead of washing out the excess nitrous acid after the diazotization, as in the conventional procedure, the effect of any such excess nitrous acid is eliminated by the addition of a reagent to the same bath and the developer is added at once, thus eliminating the draining and washing steps after diazotization which are necessary in the conventional method. The drum is then drained for the first time after the developer has completed its reaction. At this point the skins are washed well and then fat-liquored in accordance with the usual procedure.

It will be noted that in addition to the time saved by using this process rather than the conventional method, as many as four draining and washing steps can be completely eliminated. In addition to the saving in time and reagents this also enables a considerable saving in the amount liquor of between and to l is often desirable.v

This is somewhat greater than is customary; While the optimum usually will fall within this range, more or less may be employed if the amount of color to be used makes it desirable to The temperature of the wetting outliquor" do so. is held as low as practically possible so that atno time prior to the addition oflthe developer 0m;

tion will the temperature rise above'about 70 F. A starting temperature of between about 50-60 F. is desirable. The wetting out agent itself is not particularly critical.

It may be a single al ffportions at intervals of to minutes.

den a drop in pH would cause an excess of the dye to precipitate on the outside of the leather causing cracking or "bronzing. Secondly, the acid must be one which when used with sodium nitrite will produce diazotization. Hydrochloric acid, for example, is suitable for this purpose although other acids may be used if so desired. A sufficient amount of acid should be used to low- ,er the pH to between about 3.0 and 4.0. Usually about 12% to 16% of concentrated hydrochloric acid will be sufiicient. I have found that a good practice is to add the acid in two or more Usually, an addition of about one-half to two-thirds of the acid at the first step and the balance addi I ed at the second step, will be satisfactory.

kali, such as ammonia or a mixture containing. more than one alkali, such as caustic soda and soda ash, but a suflicient quantity is used to produce a pH between about'LU and 8.5." The w'etting out is preferably carried out at around'a pH of '8.0 in order that the best penetration be obtained. Forexample, when using ammonia as the alkali, from 7% to 10%, based on weight of the skins, will sufiicei' i In adding the dye I have found that a convenient practice is to addthe cold wetting out liquor to the drum and allow it to work alone on the skins for the short length. of time it takes an operator, to dissolve the dye in a separate vessel. All thedye is then added to the drum in one stage as soon as it is dissolved. However, even this small waiting period is unnecessary. The dye solution may be made up in advance and added to the drum immediately after adding the wetting out liquor with equally good results in the final product. r

In the process of the present invention", this combined wetting out and dye penetrationfstep is in sharp contrast to the conventional process. In the past the dye penetration has been carried out hot and preferably in two stages According to the present invention I have found that excellent penetration and color depth may-be had in the cold, in one stage, and, as notedabove, without previously wetting out the skin's. In addition to the time saved by thus combining the 'two steps, the leather isnot subjected to a long'treatment in contact with hot alkali and the necessity ,for large quantities of ice to coo the skins is completely eliminated. V y j Any of a number of dyes may be used in this process, for example the following dyes are among those suitable for use in my process: Developed Black BH, C. I. 401; Direct Diazo Blue BRD, C. I. 316; Diazo Blue Black RS, CI. 552; Diazine Brown M, C. I. 420; Diazine Dark GreenG, C. I. 583; and Diazo Fast Yellow 2 G, 0.1. 654', and Calcomine GreenGNL, C. I. 594. These may be added to the stock in the drum in the form of a concentrated solution and should be thoroughly worked during the addition. A period of from 30-45 minutes is usually sufiicient for a complete wetting out and penetration of the color' into the skin. If desired, supplemental coloring matter may be usedto modify the shade of the finished product, but careshould be taken to'select'for this purpose, dyes or colors which will withstand a diazotization process. 7 V i It is customary to add an acid to exhaust the dye on the leather and acid is necessary for the diazotization step. In adding this acid two points must be considered. The solution, before adding the acid, is at a pH of about 8.0. First, too sudthe dry LFor. the diazotization of the dye, a suflicient quantity of sodium nitrite is now added. About one-tenth to one-fifth as much sodium nitrite as dye is usually suificient. In som cases a smaller amount does the work quite as well. There is a disadvantage in adding any appreciable amount more than is necessary since all the excess nitrous acid must be neutralized or destroyed later. Two other points should be kept in mind during the addition of the nitrite. First, the temperature of the bath should be below about 70 F. to obtain the best results. Secondly, the nitrite should be separately dissolved and added slowly as a cold solution. If the nitrite is added too suddenly or the temperature at the time of the addition is too high, an undesirable localized reaction takes place. Although for best results it is desirable to hold the temperature of diazotization as near 7 0? F. as possible, the process is not so limited. Acceptable results may b obtained using a temperature as high as about F. About 15 to 30 minutes should be allowed for carrying out the diazotization; usually 20 minutes will be found to be a satisfactory period. It should be noted, however, that it is not necessary to add the nitrite at this point in the process. It might have been added with the dye or during the time the dye is being exhausted on th leather. Since, however, there is no particular advantage in so doing, it is easier to add the nitrite separately after the dye has been exhausted.

The nitrous acid formed during the diazotization step is injurious to most developers and as pointed out, the acid is removed by washing in the conventional practice. I have found, however, that it is suflicient that the eifect of the excess acid be eliminated before adding the developers. One method of eliminating the effect is by adding directly to the bath some reagent which will destroy the nitrous acid. These reagents maybe any compounds which will react with the nitrous acid to produce by-products which will not interfere with the subsequent developing step. Many compounds containing amino or amido groups are suitable. For example, any primary aliphatic acted with the nitrous acid should be on which is incapable of diazotization so'thatno off-shade color will be produced.v However, the pH of the bath at this point in the process is low enough so that very little penetration of the leather can take place. Therefore, a compound may be used which will eliminate the excess nitrous acidby being diazotized may beused if desired, since most of the additional diazo which may be formed in this way will remain on the surface of the leather and may be washed off later, even though it may be subsequently developed. This is particularly true in those cases where the. leather is being dyed a sufficiently dark color so that slight changes in shade will not be readily noticeable.

If desired, however, the effect on the developer of any excess nitrous acid may be overcome by adding a sufiicient amount of alkali such as ammonia so that all the nitrous acid will b in the form of a nitrite. The particular alkali used is not critical but ammonia is preferable because of its volatility. If this is done, only a part of the alkali should be added alone. The remainder may be added with the developer in order that the bath pH will notbe sufliciently high to destroy the diazonium salt before the developer is added. The pH should not be allowed to go above from about 5.0 to 6.0 before the developer is added.

The particular developer or compound which is added is not particularly critical so far as a process itself is concerned, but it is chosen for its known ability to produce a particular shade of color with the dye being used. As illustrative examples of coupling compounds suitable for use in this process are: beta naphthol, aminodiphenylamine, 2-amino 8 naphthol-6-sulfonic acid, ethyl-beta-naphthy1amine, m-phenylenediamine, m -toluylenediamine, resorcinol, nitrobenzidine and 1-phenyl-3-methyl-5-pyrazolone.

In adding the developer, attention must be given to whether or not the nitrous acid has beenreacted to form harmless products or neutralized with an alkali. If, for example, the reaction procedure was used, sufficient alkali can be added with the develop-er to produce a resultant pH between about 4.0 and 6.5 if desired. Again ammonia is a suitable alkali for this purpose. If, however, the nitrous acid was neutralized rather than destroyed, a slightly greater amount of alkali should be added to insure the desired result, for example, a resultant pH of 6.8 to 7.3 should be finally produced. In this case. however, the ammonia preferably is not added with the developer but rather at intervals over the to minutes which is usually allowed for complete development to take place.

It is not necessary that the developer be added only at this point in the process, if the developer is one which can withstand the diazotization process, it may be added at any point throughout the procedure. For example, beta oxynaphthoic acid, or the benzidide or phenetidide of acetoacetic acid may be used in this way.

As Was noted above, the tank drum is emptied for the first time when the developing is complete; the drum is drained and the skins washed. thoroughly with warm water. If necessary, a sufficient quantity of a moderately weak acid, for example, acetic acid may be added to the last wash water to bring the pH of the dyed skins down to about 4.0 to 6.0. The particular final pH. of the skin varies according to the personal opinion of different tanners. However, any point within this range is usually adequate for practical purposes.

As a final step the washer skins may be sub- 6 iected to any. conventional fat-liquor procedure. If a further slight change in the shade is desired, small quantities of acid or direct dyes may be applied by including them in the fat liquor.

While the above procedure has been outlined using an amino azo dye and a second amino grou isLbeing diazotized in situ, it is not meant to limit the invention in this respect. If it becomes desirable to do. so, any compound containing'one or more radicals capable of being diazotized. and coupled to produce a fast color and capable of being exhausted on the skin may be used. In so doing, only a part of all of the diazotizable groups may be reacted.

The invention will be more fully explained in connection with the following examples which are meant to be illustrative only and not to limit the invention. The parts are by weight unless otherwise noted.

Example 1 parts of chrome tanned calfskin were placed in a rotatable drum and treated at 55 F. with about 1200 parts of water containing 10.0 parts of concentrated ammonia and 0.5 part of soda ash while making up a solution containing 15 parts of Calcomine Diazo Black BTCW, C. I. l01,,and 2.5 parts of Calcomine Green GNL, C. I. 594., which was cooled, added to the drum and allowed 40 minutes to penetrate the skins. 10 parts of 33% hydrochloric acid were added and run for 30 minutes, after which 6 additional parts of 33% hydrochloric acid were added and run for another 30 minutes. The temperature was maintained below 70 F. At this point 1.87 parts of sodium nitrite were dissolved in water, cooled to 70 F. and run in slowly over a period of 20 minutes, at the end of which time a solution containing 7 parts of ammonium sulfamate was added and run for 15, minutes. Four parts of meta toluylene diamine were dissolved in water and. added to a solution containing 7 parts of ammonium hydroxide and added over a period of 20 minutes, at the end of which time, a pH of 5.5 was obtained. The liquid was drained from the drum at this time and the skins washed three times with waterat about F., after which they were finished by being 'fat-liquored for 30 minutes with a solution containing about 4% sulfonated' cod liver oil.

Example 2 The procedure of Example 1 was repeated, but a phenetidide of acetoacetic acid was substituted for the meta toluylene diamine developer and was added with the dye. A final product was obtained having the same satisfactory color characteristics of the suede produced in Example 1.

Example 3 100 parts of tanned kid skins were placed in a rotating drum and treated at about 50 F. with 1500 parts water containing 9 parts of ammonia and 0.42 part of soda ash while a separate, concentrated, water solution containing 18 parts of Calcomine Diazo Black BTCW, C. I. 401, and 2 parts of Calcomine Green GNL, C. I. 594, was being made up and cooled to 70 F. The dye solution was added to the drum and allowed to run for 40 minutes after which 9 parts of 33% hydrochloric acid were added and run for 30 minutes. An additional 9 parts of 33% hydrochloric acid were then added and run for 30 minutes more, after which 2.5 parts of sodium nitrite were added and run for 25 minutes to complete the diazo- 7 tization, To overcome the effect of any remainmg nitrous acid 6.25 parts of concentrated ammonium hydroxide were added and allowed to run for about minutes at which time a cool solution containing 3.75 parts of meta toluylene diamine developer and an additional 5.2 parts I of ammonium hydroxide was added. Twentyfive minutes were allowed for the development to be completed at which time the drum was drained and the skins washed and fat-liquored as in Example 1. It was found that the addition of the ammonium hydroxide had prevented any excess nitrous acid from having a deleterious effect on the developer.

Example 4 100'parts of tanned kid skins were placed in a rotating drum and treated at 52 F. with 1500 parts of water containing parts of concentrated ammonium hydroxide and 0.5 part of soda ash. A previously prepared dye solution containing 16 parts of Calcomin Diazo Black BTCW, C. I. 401, and 2.5 parts of Calcomine Green GNL, C. 1.594, was promptly added and the Whole mixture rotatedfor one-half hour. 10 parts of 33% hydrochloric acid were then added and the drum rotated for an additional half-hour after which 2.5 parts of sodium nitrite were added and the drum rotated 25 minutes more for the diazotization to becom complete. To eliminate the possible effect of any remaining nitrous acid on the developer, 10 parts of 31% monomethylamine were then added and the drum run for 5 minutes. Four parts of metatoluylene diamine in a water solution containing 6.5 parts of ammonium hydroxide were added in successive small portions over about a twenty minute period with the drum being rotated between additions. The residual liquid was drained from the drum and the skins washed with warm water and the skins were finished with a thirty-minute treatment in a fatliquor bath.

I claim:

1. A single bath process for dyeing leather which comprises preparing an aqueous solution of a compound having at least one diazotizable group and capable of being exhausted from the solution upon the leather, said solution having a pH of about 7.0-8.5; thoroughly wetting the leather to be dyed in a bath of the solution at about 50-60 F.; adding to the bath about one half to two-thirds the quantity of a strong mineral acid required to produce a pH of from about 3.0-4.0, adding the remaining acid after about 20-40 minutes and adding to'the bath a slight excess over th quantity of a metal nitrite required to form nitrous acid and diazotize the diazotizable group.

2. A method according to claim 1 in which the compound is an amino-azo dye.

3. A single bath process for dyeing leather which comprises preparing an aqueous solution of a compound having at least one diazotizable group and capable of being exhausted from the solution upon the leather, said solution having a pH of about 7.0-8.5; thoroughly wetting the leather to be dyed in a bath of the solution at about -60 F.; adding to the bath about onehalf to two-thirds the quantity of a strong mineral acid required to produce a pH of from about 3.0-4.0, adding the remaining acid after about 20-40 minutes; adding to the bath an alkali metal nitrite, in amount slightly in excess of the quantity required to form nitrous acid and diazotize the diazotizable group; allowing sufficient time for the diazotization of the diazotizable group to become substantially complete; adding to the bath a reagent capable of eliminating the eifect upon a subsequently-added developer of any residual nitrous acid after diazotization; adding'a develop er and agitating the bath for suflicient time to insure coupling of the developer with the diazo group, whereby the desired color is produced as a substantially insoluble compound before the leather is subjected to any draining and washing operation 4. A'method according to claim 3 in which the reagent is a compound capable of reacting with the nitrous acid to form products having no eifect on the developer.

5. A method according to claim 3 in which the reagent is a compound capable of neutralizing the nitrous acid.

6. A method according to claim 3 in which the reagent contains an undiazotizable amino group capable of reacting with the nitrous acid to form products having no effect on the developer;

7. A method according to claim 3 in which the reagent contains a diazotizable group.

reagent is ammonium hydroxide.

FOSTER LEWIS PEPPER. 

